1. Field of the Invention
The present invention relates to an electronic endoscope system having a special imaging function such as autofluorescence imaging (AFI) and narrow band imaging (NBI).
2. Description Related to the Prior Art
In a medical field, diagnosis and treatment using an electronic endoscope system are widely carried out in recent years. In the electronic endoscope system, while white light (normal light), which ranges from a blue wavelength band to a red wavelength band, is applied to the inside of a patient's body cavity, an image sensor such as a CCD captures an image of the light reflected from an internal body part. The captured image is displayed on a monitor. The electronic endoscope system can image the inside of the human body cavity in real time, and facilitates the accurate diagnosis and the effective treatment.
The image (normal image) captured under the normal light shows an overview of the internal body part, but cannot clearly show a capillary blood vessel, an underlying blood vessel, a pit pattern, and irregularities in surface tissue such as a depression or a lump. Since a pathologic lesion is sometimes hidden in such a portion or tissue, it is desired that the capillary blood vessel or the irregularities can be clearly seen in an endoscopic image.
As a method for imaging a tumor lesion including a cancer, for example, autofluorescence imaging (AFI) is known as described in US Application Publication No. 2009/0036743 (corresponding to Japanese Patent Laid-Open Publication No. 2009-34224). In the AFI, special light having a specific wavelength is applied as excitation light to the internal body part, and the image sensor captures an image of autofluorescence that is emitted from an endogenous fluorescent substance of living body tissue in response to the excitation light. According to the AFI, the intensity of the autofluorescence emitted from tumor tissue is weaker than that from normal tissue. Through the use of this property, the tumor lesion is colored differently from a normal portion in a special image. Thus, the tumor lesion is clearly distinguished in the special image, though it is hard to see in the normal image.
Narrow band imaging (NBI) is also known as a method for clearly imaging a superficial blood vessel, which is positioned in the shallow depth of the living body tissue, by application of special light having wavelengths in a specific narrow band, as described in Japanese Patent Laid-Open Publication No. 2001-170009. In the NBI, the superficial blood vessel is distinguished by taking advantage of a light absorbing property of the blood vessel that occurs upon application of the special light and a light scattering property of the living body tissue around the blood vessel. The special image facilitates finding out a lesion that is hard to find out in the normal image.
In a special imaging function such as the AFI and NBI, there is a need to obtain an optimal endoscopic image in accordance with various purposes of the image diagnosis. For example, in the case of trying to find out the lesion in the bright endoscopic image on a whole, the image requires enough intensity even in a far view in which a distal end portion of an electronic endoscope is away from the body part to be imaged. In the case of trying to find out the lesion from a minute portion of the image such as a clot in the blood vessel, the image requires resolution high enough to clearly discern the minute portion even in the far view. However, neither the US Patent Application Publication No. 2009/0036743 nor the Japanese Patent Laid-Open Publication No. 2001-170009 discloses or even suggests an electronic endoscope system that can obtain an optimal endoscopic image in accordance with various purposes.